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Chloë Grace Moretz has 30,000 followers on Twitter, but she is not allowed to wear high heels, not even to the premieres of her movies. In her latest, Let Me In, the 13-year-old gives a transfixing, delicately intuitive performance as Abby, an ancient vampire trapped in the inconvenient shell of a child's body. She has seen some "really beautiful" snippets of Let the Right One In, the 2008 Swedish film that inspired director Matt Reeves' American remake, but not the whole R-rated film. Her parents, McCoy (Mac) and Teri Moretz, are strict about such things. Chloë does hope that in a few years they will soften their stance on the issue of pierced ears, but she is philosophical about making do with clip-ons.

"I'm a girl," Chloë says. "I'm not 16. I'm not 20. I'm definitely 13. I get told that all the time." She shrugs, but it is not the shrug of an annoyed teen. She is unfailingly polite. It is the c'est la vie shrug of a professional, sitting in the Los Angeles office of her publicist. (See pictures of the youngest actresses nominated for an Oscar.)

Parental restrictions are something Chloë talks about a lot, both in interviews and on the video blogs she occasionally makes with one of her four brothers, Trevor, a 24-year-old look-alike who serves as her acting coach and works in movies as Trevor Duke. But it's difficult to decide whether these are the simple laments of an almost adolescent or a pre-emptive strike against those who consider her career to date an offense against innocence itself. There she was in the remake of The Amityville Horror at 6, conveying Salingeresque wisdom beyond her years in Diary of a Wimpy Kid and (500) Days of Summer and playing a foulmouthed killing machine named Hit-Girl in last spring's ultraviolent Kick-Ass. Let Me In is emotionally the darkest of them all  yet another horror movie for a young actress whose filmography is already half horror, even if the movie looks and feels a lot less like Amityville than it does Carrie, Brian De Palma's unforgettable rendering of adolescent cruelty.

Whatever the case, reminders of her age are needed. Children who are capable of the performances Chloë gives are flummoxing. We express amazement, and then we worry about the unnaturalness of it all. In Let Me In, for the first time, Chloë tackles a role that bears some resemblance to her own peculiar place in the world. Abby is worldly, with 250 years of experience, but even as a demon, she has the vulnerability of a child and faces society's restrictions; 12-year-olds can't just run around killing people. Instead, her "father" (Richard Jenkins) hunts and disposes of bodies for her. There are hints of pedophilia, although the references are more oblique than in the original. It's a tragic story, as close as our vampire-crazed society has come to a realistic depiction of what a vampire's life might be like. At its heart is the love story between Abby and a bullied boy (Kodi Smit-McPhee, who endured The Road last year) who is also friendless and 12 but won't be an adolescent for long. (See TIME's review of Let Me In.)

Neither will Chloë, of course, but therein lies the problem. She is not just maturity in a cute package, like the young Jodie Foster or Tatum O'Neal. She is a gorgeous girl, with the kind of oversize cupid's bow of a mouth (inherited from her mother) that  even when she's spitting the worst obscenities known to man, as she did, to audiences' horror, in Kick-Ass  suggests a future sensuality that the world can't help being attracted to. She's like a more skilled version of Brooke Shields in Pretty Baby. Just looking at her incites guilt.

When the "Where were the parents?" outrage over Kick-Ass hit last spring, Chloë's parents were, in fact, right there  being supportive of what seemed to them like a good opportunity. To the media, Teri Moretz pointed out the hypocrisy of being more upset by her daughter's swearing onscreen than by her gleefully killing people. Chloë, the family said, was capable of differentiating between fact and fiction. Kick-Ass has undeniably been great for her career. She just signed up for an adaptation of the cult comic Emily the Strange, and she's been shooting Martin Scorsese's Hugo Cabret in London and Paris. She's been gone for months, so it's no wonder that her father took a day off from his Beverly Hills plastic-surgery practice (he relocated from Atlanta in 2005, just as Chloë's career got serious) to spend time with his daughter during her press interviews. Clean-cut and still speaking with the soft North Carolina twang of his youth, he gives an impression of sunny stability.

Mac is aware that his daughter has been favorably compared to Foster and Natalie Portman ("We just file that away," he says placidly), attributes Chloë's extraordinary talent to a gift from God and gracefully sidesteps controversy. When Lindsay Lohan's name is introduced with regard to the pitfalls of child stardom, he says only, "Bless her heart," with a sincerity that makes you feel dirty for bringing it up. Asked whether he has seen any impact on his daughter from all these dark parts  nightmares, for instance?  he evades with endearing stories about tiny Chloë memorizing lines even before she could read.

Chloë is more willing to answer the question directly. "I've never been scared or affected by anything I ever do," she says. "I never even go into a funk when I do a crying scene, you know? Because it's fun to me." She likens herself to an athlete or a dancer and says that, while "God definitely gave me something," she works hard to refine her talent. She created a diary for Abby, trying to imagine what goes on in her mind, and by the time of her audition (a tape of which was leaked on YouTube) she already had an uncanny grasp on the character. Chloë gives constant credit to her brother Trevor for this. "The way I like to put it is, it's like a painting," she says. "I draw the outline, and he fills it in and makes it perfect." (See TIME's review of Kick-Ass.)

She does not read her own press, considering it neither fun nor helpful. (She is sweet and savvy enough to say kind things about being interviewed: "Press is cool. I like it, to a point.") But innocent though she may be, she's not oblivious to the downsides of living an adorable existence in public. In one of last year's rambling, chatty vlogs, Trevor and Chloë call for questions from fans. "Nothing too personal," Trevor says. "'Cause if you're creepy, I'm going to edit it and delete it, and you won't get heard." He indicates his little sister. "Because she's 12, O.K.?" Chloë opens her eyes wide and puts on a winning expression of mock horror. Maybe it's those four big brothers, but the girl with the scary talent seems to feel as safe as houses.

This article originally appeared in the October 11, 2010 issue of TIME.